Rear projection screen

ABSTRACT

A transmission type screen embodies a glass or plastic support having a color quality and ambient light control layer applied to the viewing side of the support. The layer comprises a dispersion of gelatin, fine particles of chlorinated diphenyl resin and a number of water-soluble dyes such as Toluidine Blue, Brilliant Acid, Cyanine Blue, Fast Light Red, Superchrome Yellow and Ethyl Orange. Such a screen structure provides an appropriate color temperature or color quality control and effectively eliminates the ambient light incident on the screen, thereby enhancing image contrast.

United States Patent DePalma [451 Apr. 11, 1972 1541 REAR PROJECTIONSCREEN 2,443,918 6/1948 Lahousse et a1. ..350/126 2,596,049 5/1952Siezen ....350/127 [721 napalm, 2,726,573 12/1955 Maloff ..350/127 [73]Assignee: Eastman Kodak Company, Rochester,

N.Y. Primary Examiner-Samuel S. Matthews Assistant Examiner-Richard M.Sheer [22] Wed: 1970 Attorney-W. H. J. Kline, P. R. Holmes and L. F.Seebach 21 A 1.N 69863 I 1 pp 0 I 57 ABSTRACT 52 U.S.Cl..350/l26,161/3.5 Atransmissiontypescreenembwiesaglassorplasficsuppo" 51Int. Cl. ..G03b 21/60 having quality and ambient Comm layer applied [58]Field ofSearch ..350/126 127 129- 161/35 the viewing Side of SUPP Thecomprises dispersion of gelatin, fine particles of chlorinated dl'phenylresin and a number of water-soluble dyes such as Toluidine [56]References CM Blue, Brilliant Acid, Cyanine Blue, Fast Light Red, Su-UNITED STATES PATENTS perchrome Yellow and Ethyl Orange. Such a screenstructure provides an appropriate color temperature or color quality1,389,357 8/1921 Hochsteffer ..161/3.5 control and ff i l eliminates theambient m incident 1,694,706 12/1928 Herz ...l61/3.5 on the Screen,thereby enhancing image contrast 2,071,836 2/1937 Jenklns... ..106/402,287,556 6/1942 Land ..350/126 12 Claims,4Drawing Figures 2/ 20 QZC J23 22 4- 8 8 0 AMB/E/VT 0 L/GHT 911 l. 27

27 LIGHT Patented April 11, 1972 3,655,262

2Sheets-Sheat l l AMBIENT LIGHT FIG. PRIOR ART }$/5 OBSERVER AMBIENTL/GHT AEROSOL 0T LAYER D? r CHLORl/VA r50 DIPHE/VYL RES/N F 3 (AROCLOI?)-32 v SUPPORT" 'DYED GELATl/V JAMES J. DeP/JLMA INVENTOR.

TRANM/TT4NCE PERCENT Patented A rii 11, 1972 3,655,262

2 Sheets-Sheat 2 FIG 4 90 A TEST SCREEN G- EXAMPLE-8 B- EXAMPLE-2 EXAMPLE-7f// 40 ,FEXAMPL7(2} l l 1 l l l 0 400 20 4 60 60 500 20 40 60 80600 i f g' WAVELENGTH //v MILL/MICRO/VS AGE/VT REAR PROJECTION SCREENFIELD OF THE INVENTION The invention relates to projection screens andmore particularly to a rear projection screen having a layer on theviewing side which enhances the color quality of a projected image andreduces the effect of ambient light.

DESCRIPTION OF THE PRIOR ART Conventional rear projection screens have aparticular disadvantage in that they do not reject the ambient light tothe extent necessary so that the projected image is one of high contrastand of good color quality. It is well known in the art that thissituation can be somewhat improved by incorporating a light absorbingmaterial along with a particulate material in the screen for redirectingthe ambient and/or image light. In a screen in which a light absorbingmaterial is embodied in the support, a good share of the ambient lightis reflected from the surface of the screen before the absorbingmaterial has a change to absorb any significant amount of the ambientlight. As a result, little or no gain in effective ambient lightrelative to image light is realized with this technique. The ambientlight reflected from the surface of the screen is due to the scatteringtype of light redirection caused by the actual screen structure and thetype of surface on the side of the screen facing the viewer.Consequently, the projected image has low contrast, low color saturationand appears to the viewer as a washed-out image. For example, it is verydiflicult' to reproduce black in a rear projection system withoutselective attenuation of the ambient light relative to the image light.

SUMMARY OF THE INVENTION The primary object of the invention is toprovide a projection screen having improved image contrast with goodcolor quality and very little, if any, reflection to the viewer ofambient light.

Another object of the invention is to provide a rear projection screenwhich absorbs substantially all of the ambient light incident thereon,thereby presenting a color image having substantially the same contrastas the original being projected.

Still another object of the invention is to provide a rear projectionscreen having a light control layer on the viewing side of the screenwhich effectively reduces the color temperature of the original image toproduce a better balanced color image. and the ambient light incident onthe layer by absorption through continual redirection.

The above objects and advantages of the invention are attained byapplying or coating a layer on the viewing side of the screen whichcomprises a dispersion of a generally clear carrier medium, fineparticles of chlorinated diphenyl resin and a plurality oflight-absorbing dyes of different color. A specific screen structureembodies a glass or plastic support having a color quality and ambientlight control layer applied to the viewing side of the support. Thelayer comprises a dispersion of gelatin, fine particles of chlorinateddiphenyl resin and a number of water-soluble dyes such as ToluidineBlue, Brilliant Acid, Cyanine Blue, Fast Light Red, Superchrome Yellowand Ethyl Orange. It was found that such a screen structure provides anappropriate color temperature or color quality control and effectivelyeliminates the ambient light incident on the screen, thereby enhancingimage contrast.

DESCRIPTION OF THE DRAWINGS Reference is now made to the accompanyingdrawings wherein like reference numerals designate like parts andwherein:

H0. 1 is an enlarged sectional view through a conventional screen havinglight scattering particles embodied therein and showing the effect ofthe ambient light incident on the viewing surface thereof;

H6. 2 is a vertical section through a screen embodying the invention inwhich a color and ambient light control layer is applied to the viewingsurface and showing the manner in which ambient light is absorbed andredirected by such a layer;

FIG. 3 is a vertical section through a screen constructed in accordancewith the invention and showing the relation of the light absorbing layerto the screen support; and

FIG. 4 is a family of transmission-color curves showing the manner inwhich the projected image is color corrected at the screen.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A conventional rear projectionscreen 10 is shown in FIG. 1 in which the support 11 has lightscattering elements or particles 12 incorporated therein. As shown bythe arrows 13, the projected image light is incident on the back surface14 of the screen and the observer l5 views the image by looking at thesurface 16. The ambient light is shown by the lines 17, with arrowsindicating the direction of the incident light. The manner in which suchlight can be reflected from the surface 16 before it enters the support11 and can be redirected by the elements or particles 12 therein isdesignated schematically by the weighted lines. At least a portion ofthe ambient light on the viewers side of the screen is reflected asdesignated by the arrows 18. The ambient light which is refracted uponentry into support 10 is scattered when an element or particle 12 isstruck. The portion of this light that is redirected to surface 16 isagain refracted (line 18a) or totally reflected (line 1812) depending onthe angle of incidence. In any case, this type of screen returns a largeamount of the ambient light to the observer, as indicated by the weightand number of return lines 19. This results in an image of low contrastand low color saturation. The light distribution is generallysymmetrical about the projector axis and has a spread of the order of aplus or minus 20-30 or more.

Some screens use a material in which the particles embodied thereinabsorb the ambient light or a second component, which can be ascattering or non-scattering component, mixed in with the materialforming the primary component or support. This technique is only partlysuccessful in that there is always a back-scattered component from theparticles and a good share of the ambient light is reflected, asmentioned above, because the reflection occurs at the surface 16 andbefore the absorbing material has a change to become of any value. Inthis case, an essentially equal amount or more of the image light 13 isalso absorbed and therefore little or no gain in effective ambient lightrelative to image light absorption is realized.

The screen 20 shown in FIG. 2 has a dyed, transparent (non-scattering),absorbing layer 21 on the viewers side of the screen. The ambient lightis designated by lines 22 with arrows indicating the light directionand, upon striking the surface 23 of layer 21, most of this light isrefracted rather than reflected. A very small portion of the ambientlight is reflected by surface 23 as indicated by lines 27. The lighttravels through the layer 21, usually obliquely, and in most instances,the remaining light is for the most part absorbed by the dyesincorporated in the layer 21. A good share of the ambient lightremaining after the initial transit through the dye layer 21 is alsoabsorbed but in the following manner. The ambient light remaining afterthe first pass through the dye layer 21 strikes the screen particles 24and is redirected more or less randomly in all directions, so that asignificant fraction might re-enter the dyed layer 21 due to theback-scattering in all directions. The light which has re-entered layer21 in this manner again travels through the dye layer 21 and has anotherchange to be absorbed and substantially reduced (lines 28). It should bepointed out that the spreading of the back-scattered ambient lightallows a relatively large share of the light to go through the dye layerat high angles, thus traveling through proportionately more of the dyelayer and, equally important, strikes the dye layer-air surface at allangles with a good share of the light incident at angles greater thanthe critical angle. This means that most of this light is reflected backthrough the dye layer (line 29) a third time and the process is repeatedover and over.

Relatively very little of this light action occurs to the image light 25that is incident on the surface 26 of screen 20. The image light in itstransit through the screen 20 is redirected for the viewing applicationby the screen elements before going through the non-scattering absorbinglayer 21. In addition, the forward scattered light is generally muchlarger than the backward scattered light and further is incident uponthe particulate layer at, or close to, normal angles of incidence andtherefore travels through the dye layer 21 in a more normal and shorterpath than the ambient light.

All of these factors add up to a significantly more efficient screen interms of brightness, contrast and image color saturation compared to ascreen having no ambient light control or with an ambient light controlusing absorbing material in situ with the light scattering particles.

The system in the subject invention provides excellent ambient lightcontrol for a scattering type projection screen. The density of the dye,the thickness of the dye layer or the preference of optical or physicalcontrol of the dyed layer with the screen material or support depends onthe characteristics of the screen material per se. The amount and kindof ambient light, the intensity of the image light as well as otherfactors also affect the resultant image. One of the very importantadvantages of the use of a non-scattering dye layer is that while it isbeing used as an efficient ambient light control element it can also beused to control the color quality of the light in the projected image.It has proven to be desirable to correct the color temperature of thelight source used in such rear projection devices which are typicallythermal in nature and therefore too warm in color quality (2600K to3000K), to a more desirable and cooler quality (3800K to 5000K). The dyelayer 21 can accomplish this in a position relative to the screensupport as shown in FIG. 2. Also, if required, a spectral energy matchto any desired color quality can be made.

With particular reference to FIG. 3, a screen structure in accordancewith the invention is specifically set forth. A support ormaterial 30which is of a transparent material is coated on one surface thereof witha layer 31 which can be a thin film of Aerosol. The dye layer 32 is thenapplied to or coated over the Aerosol layer and some of the variouscompositions that this layer 32 can comprise are set forth in Exampleshereinbelow.

The Examples set forth hereinbelow disclose a screen structure having acolor correction and ambient light control layer with the qualitiesdescribed hereinabove. The Examples are in no way to be considered aslimitations of the invention.

EXAMPLE 1 A standard, commercially available rear projection screen, wascleaned, subbed and over-coated with a layer having a composition as setforth hereinbelow at 80.4 cc per 11 /2 inches square samples.

240 cc 15% gelatin 16.8 cc 1% Toluidine Blue 1 1.4 cc 1% Acid BrilliantCyanine Blue BLE 6.0 cc 1% Fast Light Red BA 31.2 cc 0.1% SuperchromeYellow GN 36.9 cc 0.1% Ethyl Orange Dye 319 Total Total 600 cc water tomake Approximately 180 cc of 0.10 percent Aerosol OT in water was addedto this solution as a coating aid (Aerosol OT being a registeredtrademark of American Cyanamid Co. for a wetting agent andsurface-tension depressant). After coating and drying for 24 hours, thesurface was sprayed lightly with a layer of transparent lacquer. Onpractical visual tests using a screen in a commercial film reader, itwas found the ambient light control was enhanced as evidenced by theblackness of the screen with the projection lamp off in a room with 150foot candles of ambient light. The color control was indicated bymeasurement with a color temperature meter. Color saturation wasretained in the projected image and the brightness range extended; thatis, blacks were blacker and whites were whiter when compared with astandard rear projection screen having only an ambient light absorptioncontrol coating.

EXAMPLE 2 Example 1 was repeated using a polypropylene screen, such asthat disclosed in U.S. application Ser. No. 838,716, filed July 2, 1969,now U.S. Pat. No. 3,591,253. The ambient light control and image colorwere enhanced, as in Example 1. An additional advantage was realized inthat this screen system exhibited not'only good brightness and contrastbut essentially no scintillation. The dye layer can be readily affixedto this non-scintillating type of screen.

EXAMPLES 3-6 The following formulas were used on a rear projectionscreen of the type used in Example 1 and on a polyproplyene screen ofthe type used in Example 2 to control both ambient light and colortemperature.

Ex. 3 Ex. 4 Ex. 5 Ex. 6

Gelatin 15% in water cc 80 cc 80 cc 80 cc Toluidine Blue (1%) 2.8 cc 3.5cc 4.2 cc 4.90 cc Acid Brilliant Cyanine Blue (1%) 1.9 cc 2.38 cc 2.85cc 3.33 cc Fast Light Red BA (1%) 1.0 cc 1.24 cc 1.50 cc 1.75 ccSuperchrome Yellow GN (0.2%) 5.2 cc 6.50 cc 7.80 cc 9.100 cc EthylOrange Dye 319 (0.1%) 4.48 cc 5.60 cc 6.72 cc 7.84 cc Glycerine 50% 20cc 20 cc 20 cc 20 cc Water to 200 cc 200 cc Aerosol OT0.1% 13.1 cc 13.1cc 13.] cc 13.1 cc in Water The color temperature conversion for eachscreen is in the range of approximately 2850-3400K and the seriescontains increasing amounts of non-selective, non-scattering absorptionfor controlling higher ambient light levels. These layers all showedimproved contrast and brightness range.

EXAMPLE 7 The solution of Example 5 was diluted to 300 cc total and theamount of glycerine was increased to 30 cc. This solu-tion was coated on(1) a specular surfaced screen of the type used in Example 1, and (2) asemi-matte overcoating sprayed over the dye layer on a screen of thetype used in Example 1, both being cleaned and subbed prior to coating.After drying, the screens were placed in experimental viewers andcompared with a conventional coated screen as a test screen. It wasnoted the ambient light was reduced considerably and the image colorquality was much enhanced.

EXAMPLE 8 Two 8 X 10 inches optically flat glass plates were coated onone surface with a dispersion of a standard Aroclor resin in gelatin asdescribed in US. Ser. No. 814,006, filed Apr. 7, 1969; on the oppositesurface of one glass plate, which surface will be the front surface ofthe screen, a layer of dyes in gelatin of the following formula wascoated using 48.6 cc of the solution for the plate. (Aroclor is aregistered trademark of Monsanto Chemical Co. for a resin used to impartmoisture and chemical resistance.)

80 cc 15% gelatin in water 0.88 cc 1% Toluidine Blue 0.60 cc 1% AcidBrilliant Blue BLl 0.32 cc 1% Fast Light Red BA 1.64 cc 0.1% SuperchromeYellow 1.40 cc 0.1% Ethyl Orange 20 cc 50% Glycerine Water to 200 cc,then 1459 of 0.1 percent Aerosol was added as a coating aid.

The coating was dried and then sprayed with a layer of transparentlacquer. The plates were then assembled with a layer of silicone rubbertherebetween as described in U.S. Ser. No. 814,006 with the dye layer onthe viewing side of the screen. The plates were then mounted in theorbiting device of U.S. Ser. No. 813,936, filed Apr. 7, 1969, and set inmotion. The results were similar to those reported above andparticularly to those noted in Example 2.

EXAMPLE 9 Example 8 was repeated except that the dye layer was coated inhalf the concentration on each glass plate, so that half the dye layerwas, in effect, on the inside of the viewer and orbited with the rearplate forming the screen. The lacquer overcoat was omitted from the rearplate as no protection was needed. The results noted were substantiallythe same as those of Example 8.

EXAMPLE 10 A glass plate was cleaned and Aerosol OT in water was firstapplied to a surface of the plate. A layer having a composition as setforth hereinbelow was coated on the prepared surface.

436.78 cc Gelatin 260.72 cc Aroclor 62.05 cc 1% Aerosol OT 4.10 cc 1%Toluidine Blue 27.34 cc 1/ 10% Acid Brilliant Cyanine Blue BLl 15.04 cc1/l0% Fast Light Red BA 7.67 cc l/ 10% Superchrome Yellow ON 6.53 cc 110% Ethyl Orange 179.77 cc Distilled Water 1000.00 cc Total It was notedthat the screen did not reflect any appreciable amount of ambient lightand the image color quality was very good.

With reference to FIG. 4, curve A shows the transmittancewavelength(color) characteristics for a test screen that provided a comparisonbasis as set forth in the above examples. Such a screen comprises aglass plate having a light control layer coated on one surface thereof.Such a layer comprises a dispersion of gelatin and chlorinated diphenylresin (Aroclor). The screen with such a layer transmits about 70-85percent of the light incident thereon, the higher percentage being inthe frequency of the yellow-orange-red colors. As a result, white doesnot appear as such in the projected image, but rather yellowish.Likewise, black appears to be hazy and not a true black. When thereflected ambient light is added to such a projected image, the contrastis still further reduced.

Curves B-F disclose light control layers in accordance with theinvention wherein more light is transmitted in the blue frequency range.Although less light is actually transmitted, the contrast is enhancedbecause the yellow-orange-red frequencies do not predominate, thecontrast being enhanced because of the absorption of the ambient light.

Curve G discloses a screen which transmits primarily in the blue-greenfrequency range with a higher percentage of total transmittance.However, this screen comprises two glass plates which are orbitedrelative to one another and, hence, a screen of somewhat differentstructure is set forth in this example.

ln instances where the projection screen is such that it permits a muchhigher than normal ratio of forward to back-scattered light in thescreen material, it may be advantageous to use a non-scattering dyesystem in a separate layer on the screen surface facing the lightsource. Also, it is possible that a non-scattering layer can be used onboth the front and back surface with a factor of absorptiondifferential.

The screen support can consist of plastic particles embedded in a clearresin coated on glass or a suitable transparent, plastic material, suchas vinyl, methylacrylate, etc., or the carrier resin itself may beself-supporting. It is conceivable therefore that the non-scattering dyelayer 32 can be dispersed in any number of non-scattering carrier mediasuch as gelatin, methylacrylate, glass, polystryene, etc., andsubsequently coated on or placed as a separate sheet in physicalcontract with the screen support 30. Also, the surfaces of thenon-scattering dye layer 32 can be made either specular, semispecular ordiffuse depending on the nature of the projection situation to beaccommodated.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention.

Iclaim:

l. A screen material for transmission type projection screens havingcolor quality and ambient light control comprising a dispersion of agenerally clear carrier medium, fine particles of chlorinated diphenylresin and a plurality of light absorbing dyes of different color.

2. A screen material in accordance with claim 1 wherein said carriermedium is gelatin.

3. A screen material in accordance with claim 1 wherein said carriermedium is a generally transparent plastic material.

4. A screen material in accordance with claim 1 wherein said carriermedium is methacrylate.

5. A screen material in accordance with claim 1 wherein said carriermedium is polystyrene.

6. A screen material in accordance with claim 1 wherein said lightabsorbing dyes are blue, light red, yellow and orange in color.

7. A rear projection screen comprising a generally transparent supportand a color quality and ambient light control layer applied to at leastthe viewing side of said support, said layer comprising a dispersion ofa generally clear carrier medium, fine particles of chlorinated diphenylresin and a plurality of light absorbing dyes of different color.

8. A rear projection screen in accordance with claim 7 wherein saidsupport is glass.

9. A rear projection screen in accordance with claim 7 wherein saidsupport is a generally transparent plastic material.

10. A rear projection screen in accordance with claim 7 wherein saidcarrier medium is gelatin.

11. A rear projection screen in accordance with claim 7 wherein saiddyes are blue, light red, yellow and orange in color.

12. A rear projection screen comprising a generally transparent plasticsupport and a color quality and ambient light control layer applied toat least the viewing side of said support, said layer comprising adispersion of gelatin, fine particles of chlorinated diphenyl resin anda plurality of light absorbing dyes which are Toluidine Blue, BrilliantAcid Cyanine Blue, Fast Light Red, Superchrome Yellow and Ethyl Orangein color.

2. A screen material in accordance with claim 1 wherein said carriermedium is gelatin.
 3. A screen material in accordance with claim 1wherein said carrier medium is a generally transparent plastic material.4. A screen material in accordance with claim 1 wherein said carriermedium is methacrylate.
 5. A screen material in accordance with claim 1wherein said carrier medium is polystyrene.
 6. A screen material inaccordance with claim 1 wherein said light absorbing dyes are blue,light red, yellow and orange in color.
 7. A rear projection screencomprising a generally transparent support and a color quality andambient light control layer applied to at least the viewing side of saidsupport, said layer comprising a dispersion of a generally clear carriermedium, fine particles of chlorinated diphenyl resin and a plurality oflight absorbing dyes of different color.
 8. A rear projection screen inaccordance with claim 7 wherein said support is glass.
 9. A rearprojection screen in accordance with claim 7 wherein said support is agenerally transparent plastic material.
 10. A rear projection screen inaccordance with claim 7 wherein said carrier medium is gelatin.
 11. Arear projection screen in accordance with claim 7 wherein said dyes areblue, light red, yellow and orange in color.
 12. A rear projectionscreen comprising a generally transparent plastic support and a colorquality and ambient light control layer applied to at least the viewinGside of said support, said layer comprising a dispersion of gelatin,fine particles of chlorinated diphenyl resin and a plurality of lightabsorbing dyes which are Toluidine Blue, Brilliant Acid Cyanine Blue,Fast Light Red, Superchrome Yellow and Ethyl Orange in color.